Abstract
Variation in the melanocortin-1 receptor (Mc1r) is associated with pigmentation diversity in wild and domesticated populations of vertebrates, including several species of birds. Among domestic bird species, pigmentation variation in the rock pigeon ( Columba livia ) is particularly diverse. To determine the potential contribution of Mc1r variants to pigment diversity in pigeons, we sequenced Mc1r in a wide range of pigeon breeds and identified several single nucleotide polymorphisms, including a variant that codes for an amino acid substitution (Val85Met). In contrast to the association between Val85Met and eumelanism in other avian species, this change was associated with pheomelanism in pigeons. In vitro cAMP accumulation and protein expression assays revealed that Val85Met leads to decreased receptor function and reduced cell surface expression of the mutant protein. The reduced in vitro function is consistent with the observed association with reduced eumelanic pigmentation. Comparative genetic and cellular studies provide important insights about the range of mechanisms underlying diversity among vertebrates, including different phenotypic associations with similar mutations in different species.
Highlights
Variation in the melanocortin-1 receptor (Mc1r) is associated with pigment variation across a phylogenetically broad range of wild and domestic populations of vertebrates, including mammals, fishes, reptiles, and birds (e.g., [1,2,3,4])
We identified 7 variants in the coding sequence of Mc1r in rock pigeons (Genbank accession numbers KF234242KF234252)
The Val85 residue is highly conserved across vertebrates (Table 2), suggesting that it is probably important for normal Mc1r function [30]
Summary
Variation in the melanocortin-1 receptor (Mc1r) is associated with pigment variation across a phylogenetically broad range of wild and domestic populations of vertebrates, including mammals, fishes, reptiles, and birds (e.g., [1,2,3,4]). Birds exhibit widespread color variation among species, and less commonly, they show substantial variation within species In the latter cases, amino acid substitutions in Mc1r are associated with color polymorphisms in several distantly related species, including both wild [5,6,7,8,9,10,11] and domestic populations [12,13,14,15,16,17]. We test the functionality of a mutant allele of Mc1r in pigeons, and discuss our findings in light of studies of this gene in other vertebrates
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